diff --git a/packages/jest-haste-map/src/crawlers/watchman.js b/packages/jest-haste-map/src/crawlers/watchman.js
index 2c79d289d5cf..9125911e5b5b 100644
--- a/packages/jest-haste-map/src/crawlers/watchman.js
+++ b/packages/jest-haste-map/src/crawlers/watchman.js
@@ -11,6 +11,7 @@
 import type {InternalHasteMap} from 'types/HasteMap';
 import type {CrawlerOptions} from '../types';
 
+import normalizePathSep from '../lib/normalize_path_sep';
 import path from 'path';
 import watchman from 'fb-watchman';
 import H from '../constants';
@@ -104,7 +105,7 @@ module.exports = function watchmanCrawl(
 
             clocks[root] = response.clock;
             response.files.forEach(fileData => {
-              const name = root + path.sep + fileData.name;
+              const name = root + path.sep + normalizePathSep(fileData.name);
               if (!fileData.exists) {
                 delete files[name];
               } else if (!ignore(name)) {
diff --git a/packages/jest-haste-map/src/index.js b/packages/jest-haste-map/src/index.js
index 50aa9321d165..571285386e68 100644
--- a/packages/jest-haste-map/src/index.js
+++ b/packages/jest-haste-map/src/index.js
@@ -38,6 +38,7 @@ import HasteModuleMap from './module_map';
 import getMockName from './get_mock_name';
 import getPlatformExtension from './lib/get_platform_extension';
 import nodeCrawl from './crawlers/node';
+import normalizePathSep from './lib/normalize_path_sep';
 import watchmanCrawl from './crawlers/watchman';
 import worker from './worker';
 
@@ -616,7 +617,7 @@ class HasteMap extends EventEmitter {
       root: Path,
       stat: {mtime: Date},
     ) => {
-      filePath = path.join(root, filePath);
+      filePath = path.join(root, normalizePathSep(filePath));
       if (
         this._ignore(filePath) ||
         !extensions.some(extension => filePath.endsWith(extension))
diff --git a/packages/jest-haste-map/src/lib/__tests__/normalize_path_sep.test.js b/packages/jest-haste-map/src/lib/__tests__/normalize_path_sep.test.js
new file mode 100644
index 000000000000..9f28324aa12d
--- /dev/null
+++ b/packages/jest-haste-map/src/lib/__tests__/normalize_path_sep.test.js
@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails oncall+jsinfra
+ */
+'use strict';
+
+describe('normalizePathSep', () => {
+  it('does nothing on posix', () => {
+    jest.resetModules();
+    jest.mock('path', () => require.requireActual('path').posix);
+    const normalizePathSep = require('../normalize_path_sep');
+    expect(normalizePathSep('foo/bar/baz.js')).toEqual('foo/bar/baz.js');
+  });
+
+  it('replace slashes on windows', () => {
+    jest.resetModules();
+    jest.mock('path', () => require.requireActual('path').win32);
+    const normalizePathSep = require('../normalize_path_sep');
+    expect(normalizePathSep('foo/bar/baz.js')).toEqual('foo\\bar\\baz.js');
+  });
+});
diff --git a/packages/jest-haste-map/src/lib/normalize_path_sep.js b/packages/jest-haste-map/src/lib/normalize_path_sep.js
new file mode 100644
index 000000000000..abd3eb06ea21
--- /dev/null
+++ b/packages/jest-haste-map/src/lib/normalize_path_sep.js
@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+const path = require('path');
+
+let normalizePathSep;
+if (path.sep == '/') {
+  normalizePathSep = (filePath: string) => filePath;
+} else {
+  normalizePathSep = (filePath: string) => filePath.replace(/\//g, path.sep);
+}
+
+module.exports = normalizePathSep;